JP6818191B1 - Power converter - Google Patents

Abstract

The power converter (1) includes a power converter (2) including a plurality of arms (5, 6) having a plurality of converter cells (7) cascaded to each other. Each converter cell (7) includes a power storage element that is electrically connected to an input / output terminal via a plurality of switching elements. The control device (3) controls the AC current according to the deviation between the detected AC current (Iac) and the AC current command value, and the individual voltage according to the deviation between the voltage of each storage element and the individual voltage command value. Take control and. The control device (3) calculates an evaluation value indicating the degree of voltage variation of the power storage element in the entire power converter (2), and when the evaluation value is larger than the threshold value, AC current control and individual voltage control The control of the power converter (2) is changed so that the arm current (Iarm) flowing through the plurality of arms (5, 6) increases while executing the above.

Description

This disclosure relates to a power converter.

Modular Multilevel Converter (MMC), in which multiple unit converters (hereinafter referred to as "converter cells") are connected in cascade, is known as a large-capacity power converter installed in the power system. Has been done. Usually, a converter cell includes a plurality of switching elements and a power storage element (typically, a capacitor).

In a modular multi-level converter, it is necessary to maintain the voltage (capacitor voltage) of the power storage element of each converter cell near the target value in order to obtain a desired control output. If the capacitor voltage deviates from the target value, the output voltage of the converter cell does not follow the command, and there is a concern that the control characteristics may deteriorate due to the unintended generation of circulating current or the like. In significant cases, in any of the transducer cells, the capacitor voltage may over-rise or under-voltage to the level of overvoltage protection or undervoltage protection, which could stop the operation of the MMC.

Normally, the capacitor voltage is controlled by the entire converter cell in the MMC (hereinafter, also referred to as "total voltage control") in addition to the capacitor voltage control for each individual converter cell (hereinafter, also referred to as "individual control"). It is generally controlled in multiple layers by balance control between a certain group (for example, arm or phase) (for example, Japanese Patent Application Laid-Open No. 2011-182517 (Patent Document 1)). See).

According to JP-A-2019-030106 (Patent Document 2), when an MMC is connected to an AC circuit such as an AC power supply and an AC load, individual control cannot be stably executed depending on the condition of the AC circuit, and the capacitor voltage is increased. The issue is that imbalance occurs. Specifically, the power conversion device described in this document is used when the AC power flowing in or out between the AC circuit and the power conversion unit is smaller than the threshold value in order to stably execute individual control. In addition to the circulating current for interphase balance control, the circulating current for individual control is passed.

Japanese Unexamined Patent Publication No. 2011-182517 Japanese Unexamined Patent Publication No. 2019-030106

When the AC power input / output between the AC circuit and the power conversion unit is smaller than the threshold value, the individual capacitor voltages are not necessarily unbalanced. The problem with the control method described in JP-A-2019-030106 (Patent Document 2) is that when the AC power input / output between the AC circuit and the power conversion unit is small, it is always controlled individually. It is in the point that the circulating current of is flowing. Therefore, even though the variation of the individual capacitor voltage is within the permissible range, there is a possibility that power is wasted.

This disclosure takes into account the above problems, and an object of the present invention is to provide an MMC type power conversion device capable of performing individual control of a capacitor voltage more stably and efficiently.

The power converter according to one embodiment includes a power converter, an alternating current detector, and a control device. The power converter includes a plurality of arms having a plurality of converter cells cascaded to each other. Each of the arms is electrically connected to the corresponding phase of the AC circuit. Each of the plurality of converter cells detects a pair of input / output terminals, a plurality of switching elements, a power storage element electrically connected to the input / output terminals via the plurality of switching elements, and a voltage of the power storage element. It has a voltage detector. The AC current detector detects the AC current flowing through the AC line connecting the AC circuit and the power converter. The control device controls the power converter. The control device includes an alternating current control unit, an individual voltage control unit, and a control change unit. The AC current control unit performs AC current control according to the deviation between the detected AC current and the AC current command value. The individual voltage control unit performs individual voltage control according to the deviation between the voltage of each power storage element and the individual voltage command value. The control change unit calculates an evaluation value indicating the degree of voltage variation of the power storage element in the entire power converter, and when the evaluation value is larger than the threshold value, while executing AC current control and individual voltage control, Change the control of the power converter so that the arm current flowing through each of the multiple arms increases.

According to the above embodiment, when the evaluation value indicating the degree of voltage variation of the power storage element in the entire power converter is larger than the threshold value, the power conversion is performed so that the arm current flowing through each of the plurality of arms increases. Change the control of the vessel. As a result, individual control of the capacitor voltage can be performed more stably and efficiently.

It is a schematic block diagram of the power conversion apparatus 1 which concerns on this embodiment. It is a circuit diagram which shows the structural example of the converter cell 7 which comprises the electric power converter 2. It is a functional block diagram explaining the internal structure of the control device 3 shown in FIG. It is a block diagram which shows the hardware configuration example of a control device. FIG. 3 is a block diagram illustrating a configuration example of the basic control unit 502 shown in FIG. It is a block diagram explaining the structural example of the arm control part 503. It is a block diagram which shows the structural example of the individual cell control unit 202 shown in FIG. It is a block diagram which shows the detailed block diagram of the individual voltage control part. It is a conceptual waveform diagram for demonstrating PWM modulation control by the gate signal generation part shown in FIG. 7. It is a block diagram which shows the structural example of the circulation current change part 810. It is a block diagram which shows the structural example of the circulating current control part including the function which changes the circulating current command value. It is a flowchart which shows the operation of the command value change command part of FIG. It is a schematic block diagram of the power conversion apparatus of Embodiment 2. FIG. 3 is a block diagram showing a configuration example of a phase adjustment device control unit that controls the operation of the phase adjustment device of FIG. 13. It is a flowchart which shows the operation example of the switch control part of FIG. It is a block diagram which shows the structural example of the transformer control part for controlling the switching of the tap of the transformer of FIG. It is a flowchart which shows the operation example of the tap changer command part of FIG. It is a block diagram which shows the structural example of the negative-phase current control part for controlling the negative-phase current supplied from a power converter to a DC circuit. It is a block diagram which shows the structural example of the AC current control part in the power conversion apparatus of Embodiment 4. It is a flowchart which shows the operation example of the command value change command part of FIG. FIG. 5 is a block diagram showing a configuration example of a generalized control changing unit of the circulating current changing unit of FIG. 10, the phase adjusting device control unit of FIG. 13, the transformer control unit 830 of FIG. 15, and the reverse phase current control unit of FIG. is there. It is a flowchart which shows the operation example of the change command part of FIG.

Hereinafter, each embodiment will be described in detail with reference to the drawings. In some cases, the same or corresponding parts are designated by the same reference numerals and the description thereof may not be repeated.

Embodiment 1.
(Overall configuration of power converter)
FIG. 1 is a schematic configuration diagram of the power conversion device 1 according to the present embodiment.

With reference to FIG. 1, the power converter 1 is composed of a modular multi-level converter including a plurality of converter cells connected in series with each other. The "converter cell" is also referred to as a "submodule", SM, or "unit converter". The power conversion device 1 performs power conversion between the DC circuit 14 and the AC circuit 12. The power converter 1 includes a power converter 2 and a control device 3.

The power converter 2 has a plurality of leg circuits 4u, which are connected in parallel to each other between the positive electrode DC terminal (that is, the high potential side DC terminal) Np and the negative electrode DC terminal (that is, the low potential side DC terminal) Nn. Includes 4v, 4w (referred to as leg circuit 4 when generically or arbitrarily).

The leg circuit 4 is provided in each of the plurality of phases constituting the alternating current. The leg circuit 4 is connected between the AC circuit 12 and the DC circuit 14, and performs power conversion between the two circuits. FIG. 1 shows a case where the AC circuit 12 is a three-phase AC system, and three leg circuits 4u, 4v, and 4w are provided corresponding to the U phase, the V phase, and the W phase, respectively.

The AC input terminals Nu, Nv, Nw provided in the leg circuits 4u, 4v, 4w, respectively, are connected to the AC circuit 12 via the transformer 13. The AC circuit 12 is, for example, an AC power system including an AC power supply and the like. In FIG. 1, the connection between the AC input terminals Nv, Nw and the transformer 13 is not shown for ease of illustration.

The high potential side DC terminal Np and the low potential side DC terminal Nn commonly connected to each leg circuit 4 are connected to the DC circuit 14. The DC circuit 14 is, for example, a DC terminal of a DC power system or other power conversion device including a DC transmission network or the like. In the latter case, a BTB (Back To Back) system for connecting AC power systems having different rated frequencies or the like is configured by connecting two power conversion devices.

Instead of using the transformer 13 of FIG. 1, it may be connected to the AC circuit 12 via an interconnection reactor. Further, instead of the AC input terminals Nu, Nv, Nw, the leg circuits 4u, 4v, 4w are provided with primary windings, respectively, and the leg circuits 4u, 4v, 4w are provided via the secondary windings magnetically coupled to the primary windings. May be connected to the transformer 13 or the interconnection reactor in an alternating current manner. In this case, the primary winding may be the following reactors 8A and 8B. That is, the leg circuit 4 is electrically (that is, DC or AC) via the connection portion provided in each leg circuit 4u, 4v, 4w such as the AC input terminals Nu, Nv, Nw or the above-mentioned primary winding. It is connected to the AC circuit 12.

The leg circuit 4u includes an upper arm 5 from the high potential side DC terminal Np to the AC input terminal Nu, and a lower arm 6 from the low potential side DC terminal Nn to the AC input terminal Nu. The AC input terminal Nu, which is a connection point between the upper arm 5 and the lower arm 6, is connected to the transformer 13. The high potential side DC terminal Np and the low potential side DC terminal Nn are connected to the DC circuit 14. Since the leg circuits 4v and 4w have the same configuration, the configuration of the leg circuit 4u will be typically described below.

The upper arm 5 includes a plurality of cascaded converter cells 7 and a reactor 8A. The plurality of converter cells 7 and the reactor 8A are connected in series. Similarly, the lower arm 6 includes a plurality of cascaded transducer cells 7 and a reactor 8B. The plurality of converter cells 7 and the reactor 8B are connected in series. In the following description, the number of converter cells 7 included in each of the upper arm 5 and the lower arm 6 is Ncell. However, Ncell ≧ 2.

The position where the reactor 8A is inserted may be any position of the upper arm 5 of the leg circuit 4u, and the position where the reactor 8B is inserted may be any position of the lower arm 6 of the leg circuit 4u. Good. A plurality of reactors 8A and 8B may be provided respectively. The inductance values of each reactor may be different from each other. Further, only the reactor 8A of the upper arm 5 or only the reactor 8B of the lower arm 6 may be provided. Further, the transformer connection may be devised to cancel the magnetic flux of the DC component current, and the leakage reactance of the transformer may act on the AC component current as a substitute for the reactor. By providing the reactors 8A and 8B, it is possible to suppress a sudden increase in the accident current at the time of an accident in the AC circuit 12 or the DC circuit 14.

The power conversion device 1 further includes an AC voltage detector 10, an AC current detector 16, and DC voltage detectors 11A and 11B as each detector for measuring the amount of electricity (current, voltage, etc.) used for control. And arm current detectors 9A and 9B provided in each leg circuit 4, and a direct current detector 17 is included. The signals detected by these detectors are input to the control device 3.

In FIG. 1, in order to facilitate the illustration, the signal line of the signal input from each detector to the control device 3 and the signal line of the signal input / output between the control device 3 and each converter cell 7 are shown. Is partially described together, but is actually provided for each detector and each converter cell 7. The signal lines between each converter cell 7 and the control device 3 may be provided separately for transmission and reception. The signal line is composed of, for example, an optical fiber.

Next, each detector will be specifically described.
The AC voltage detector 10 detects the U-phase AC voltage Vacu, the V-phase AC voltage Vacv, and the W-phase AC voltage Vacw of the AC circuit 12. In the following description, Vaccu, Vaccv, and Vacw are collectively referred to as Vac.

The AC current detector 16 detects the U-phase AC current Iacu, the V-phase AC current Iacv, and the W-phase AC current Iacw of the AC circuit 12. In the following description, Iac, Iacv, and Iacw are collectively referred to as Iac.

The DC voltage detector 11A detects the DC voltage Vdcp of the high potential side DC terminal Np connected to the DC circuit 14. The DC voltage detector 11B detects the DC voltage Vdcn of the low potential side DC terminal Nn connected to the DC circuit 14. The difference between the DC voltage Vdcp and the DC voltage Vdcn is defined as the DC voltage Vdc. The DC current detector 17 detects the DC current Idc flowing through the high potential side DC terminal Np or the low potential side DC terminal Nn.

The arm current detectors 9A and 9B provided in the leg circuit 4u for the U phase detect the upper arm current Ipu flowing through the upper arm 5 and the lower arm current Inu flowing through the lower arm 6, respectively. The arm current detectors 9A and 9B provided in the leg circuit 4v for the V phase detect the upper arm current Ipv and the lower arm current Inv, respectively. The arm current detectors 9A and 9B provided in the leg circuit 4w for the W phase detect the upper arm current Ipw and the lower arm current Inw, respectively. In the following description, the upper arm currents Ipu, Ipv, and Ipw are collectively referred to as the upper arm current Iarmp, and the lower arm currents Inu, Inv, and Inw are collectively referred to as the lower arm current Iarmn. The lower arm current Iarmn is also collectively referred to as Iarm.

(Example of converter cell configuration)
FIG. 2 is a circuit diagram showing a configuration example of a converter cell 7 constituting the power converter 2.

The converter cell 7 shown in FIG. 2A has a circuit configuration called a half-bridge configuration. The converter cell 7 includes a series body formed by connecting two switching elements 31p and 31n in series, a power storage element 32, a voltage detector 33, and input / output terminals P1 and P2. The series of switching elements 31p and 31n and the power storage element 32 are connected in parallel. The voltage detector 33 detects the voltage Vc between both ends of the power storage element 32.

Both terminals of the switching element 31n are connected to the input / output terminals P1 and P2, respectively. The converter cell 7 outputs the voltage Vc or zero voltage of the power storage element 32 between the input / output terminals P1 and P2 by the switching operation of the switching elements 31p and 31n. When the switching element 31p is on and the switching element 31n is off, the voltage Vc of the power storage element 32 is output from the converter cell 7. When the switching element 31p is off and the switching element 31n is on, the converter cell 7 outputs a zero voltage.

The converter cell 7 shown in FIG. 2B has a circuit configuration called a full bridge configuration. The converter cell 7 includes a first series body formed by connecting two switching elements 31p1 and 31n1 in series, and a second series body formed by connecting two switching elements 31p2 and 31n2 in series. The storage element 32, the voltage detector 33, and the input / output terminals P1 and P2 are provided. The first series body, the second series body, and the power storage element 32 are connected in parallel. The voltage detector 33 detects the voltage Vc between both ends of the power storage element 32.

The midpoint of the switching element 31p1 and the switching element 31n1 is connected to the input / output terminal P1. Similarly, the midpoint of the switching element 31p2 and the switching element 31n2 is connected to the input / output terminal P2. The converter cell 7 outputs the voltage Vc, −Vc, or zero voltage of the power storage element 32 between the input / output terminals P1 and P2 by the switching operation of the switching elements 31p1, 31n1, 31p2, 31n2.

In FIGS. 2 (a) and 2 (b), the switching elements 31p, 31n, 31p1, 31n1, 31p2, 31n2 are self-sufficients such as an IGBT (Insulated Gate Bipolar Transistor) and a GCT (Gate Commutated Turn-off) thyristor. An FWD (Freewheeling Diode) is connected in antiparallel to an arc-extinguishing semiconductor switching element.

In FIGS. 2A and 2B, a capacitor such as a film capacitor is mainly used as the power storage element 32. The power storage element 32 may be referred to as a capacitor in the following description. Hereinafter, the voltage Vc of the power storage element 32 is also referred to as a capacitor voltage Vc.

As shown in FIG. 1, the converter cells 7 are cascaded. In each of FIGS. 2A and 2B, in the converter cell 7 arranged on the upper arm 5, the input / output terminal P1 is the input / output terminal P2 of the adjacent converter cell 7 or the high potential side DC. It is connected to the terminal Np, and the input / output terminal P2 is connected to the input / output terminal P1 or the AC input terminal Nu of the adjacent converter cell 7. Similarly, in the converter cell 7 arranged on the lower arm 6, the input / output terminal P1 is connected to the input / output terminal P2 or the AC input terminal Nu of the adjacent converter cell 7, and the input / output terminal P2 is adjacent. It is connected to the input / output terminal P1 of the converter cell 7 or the low potential side DC terminal Nn.

Hereinafter, a case where the converter cell 7 has a half-bridge cell configuration shown in FIG. 2A and a semiconductor switching element is used as the switching element and a capacitor is used as the power storage element will be described as an example. However, the converter cell 7 constituting the power converter 2 may have a full bridge configuration shown in FIG. 2 (b). Further, a converter cell other than the configuration illustrated above, for example, a converter cell to which a circuit configuration called a clamped double cell or the like is applied may be used, and the switching element and the power storage element are also limited to the above examples. is not.

(Control device)
FIG. 3 is a functional block diagram illustrating the internal configuration of the control device 3 shown in FIG.

With reference to FIG. 3, the control device 3 includes a switching control unit 501 for controlling the on / off of the switching elements 31p and 31n of each converter cell 7.

The switching control unit 501 includes a U-phase basic control unit 502U, a U-phase upper arm control unit 503UP, a U-phase lower arm control unit 503UN, a V-phase basic control unit 502V, a V-phase upper arm control unit 503VP, and V. It includes a lower arm control unit 503VN, a W phase basic control unit 502W, a W phase upper arm control unit 503WP, and a W phase lower arm control unit 503WN.

In the following description, the U-phase basic control unit 502U, the V-phase basic control unit 502V, and the W-phase basic control unit 502W are collectively referred to as the basic control unit 502. Similarly, the U-phase upper arm control unit 503UP, the U-phase lower arm control unit 503UN, the V-phase upper arm control unit 503VP, the V-phase lower arm control unit 503VN, the W-phase upper arm control unit 503WP, and the W-phase lower arm control. The unit 503WN is also collectively referred to as an arm control unit 503.

FIG. 4 is a block diagram showing a hardware configuration example of the control device. FIG. 4 shows an example in which the control device 3 is configured by a computer.

With reference to FIG. 4, the control device 3 includes one or more input converters 70, one or more sample hold (S / H) circuits 71, a multiplexer (MUX) 72, and an A / D (Analog to). Digital) includes a converter 73. Further, the control device 3 includes one or more CPUs (Central Processing Units) 74, a RAM (Random Access Memory) 75, and a ROM (Read Only Memory) 76. Further, the control device 3 includes one or more input / output interfaces 77, an auxiliary storage device 78, and a bus 79 that interconnects the above components.

The input converter 70 has an auxiliary transformer (not shown) for each input channel. Each auxiliary transformer converts the detection signal by each electric quantity detector of FIG. 1 into a signal of a voltage level suitable for subsequent signal processing.

The sample hold circuit 71 is provided for each input converter 70. The sample hold circuit 71 samples and holds a signal representing the amount of electricity received from the corresponding input converter 70 at a predetermined sampling frequency.

The multiplexer 72 sequentially selects the signals held by the plurality of sample hold circuits 71. The A / D converter 73 converts the signal selected by the multiplexer 72 into a digital value. By providing a plurality of A / D converters 73, A / D conversion may be executed in parallel for the detection signals of the plurality of input channels.

The CPU 74 controls the entire control device 3 and executes arithmetic processing according to a program. The RAM 75 as the volatile memory and the ROM 76 as the non-volatile memory are used as the main memory of the CPU 74. The ROM 76 stores programs, setting values for signal processing, and the like. The auxiliary storage device 78 is a non-volatile memory having a larger capacity than the ROM 76, and stores programs, electric energy detection value data, and the like.

The input / output interface 77 is an interface circuit for communication between the CPU 74 and the external device.

In addition, unlike the example of FIG. 3, at least a part of the control device 3 can be configured by using a circuit such as FPGA (Field Programmable Gate Array) and ASIC (Application Specific Integrated Circuit). That is, the function of each functional block shown in FIG. 3 can be configured based on the computer illustrated in FIG. 4, or at least a part thereof can be configured by using circuits such as FPGA and ASIC. it can. Further, at least a part of the functions of each functional block can be configured by an analog circuit.

FIG. 5 is a block diagram illustrating a configuration example of the basic control unit 502 shown in FIG.
With reference to FIG. 5, the basic control unit 502 includes an arm voltage command generation unit 601. Further, the control device 3 further includes a voltage evaluation value generation unit 700 that generates the voltage evaluation value Vcg used in the arm voltage command generation unit 601.

The arm voltage command generation unit 601 calculates the arm voltage command value krefp of the upper arm and the arm voltage command value krefn of the lower arm. In the following description, krefp and krefn are collectively referred to as kref.

The voltage evaluation value generation unit 700 receives the capacitor voltage Vc detected by the voltage detector 33 in each converter cell 7. The voltage evaluation value generation unit 700 includes a total voltage evaluation value Vcgall for evaluating the total stored energy of the capacitors 32 of all the converter cells 7 of the power converter 2 from the capacitor voltage Vc of each converter cell 7. A voltage evaluation value Vcgr for each group indicating the total storage energy of the capacitor 32 of the converter cell 7 for each predetermined group is generated.

For example, the voltage evaluation value Vcgr for each group is the plurality of (2 × Necll) converter cells 7 included in each of the leg circuits 4u (U phase), 4v (V phase), and 4w (W phase). The U-phase voltage evaluation value Vcgu, the V-phase voltage evaluation value Vcgv, and the V-phase voltage evaluation value Vcgv for evaluating the total stored energy are included. Alternatively, the voltage evaluation value Vcgr for each group is replaced with or in addition to the voltage evaluation value for each leg circuit 4 (U phase, V phase, W phase), and the upper arm 5 and the lower arm 6 are used for each leg circuit 4. For each of the above, a group-by-group voltage evaluation value Vcgr for evaluating the total stored energy of a plurality of (Necl) converter cells 7 included in each arm may be included. In the present embodiment, the total voltage evaluation value Vcgal and the voltage evaluation value Vcgr for each group generated by the voltage evaluation value generation unit 700 are comprehensively referred to as the voltage evaluation value Vcg.

These voltage evaluation values Vcg are the average value of the capacitor voltage Vc of all the converter cells 7 of the power converter 2, or the value of a plurality of converter cells 7 belonging to each group (each phase leg circuit or each arm). It is obtained as the average value of the capacitor voltage Vc.

The arm voltage command generation unit 601 includes an alternating current control unit 603, a circulation current calculation unit 604, a circulation current control unit 605, a command distribution unit 606, and a voltage macro control unit 610.

The AC current control unit 603 calculates the AC control command value Vcp for making the deviation between the detected AC current Iac and the set AC current command value Iacref 0. For example, the AC current control unit 603 can be configured as a PI controller that performs proportional calculation and integral calculation with respect to the deviation, or can be configured as a PID controller that further performs differential calculation. Alternatively, it is also possible to configure the AC current control unit 603 by using the configuration of another controller generally used for feedback control.

As will be described later with reference to FIG. 19, in the case of the fourth embodiment, the AC current control unit 603 is further provided with a command value changing unit 630 for changing the AC current command value Iacref.

The circulation current calculation unit 604 calculates the circulation current Iz flowing through one leg circuit 4 based on the arm current Iarmp of the upper arm and the arm current Iarmp of the lower arm. The circulating current is a current that circulates between the plurality of leg circuits 4. For example, the circulating current Iz flowing through one leg circuit 4 can be calculated by the following equations (1) and (2).

Idc = (Ipu + Ipv + Ipw + Inu + Inv + Inw) / 2 ... (1)
Iz = (Iarmp + Iarmn) /2-Idc/3 ... (2)
The voltage macro control unit 610 has excess or deficiency of stored energy in all the converter cells 7 of the power converter 2 and between groups (each) based on the voltage evaluation value Vcg generated by the voltage evaluation value generation unit 700. The circulating current command value Izref is generated to compensate for the imbalance of stored energy between the phase leg circuits or between the arms.

For example, the voltage macro control unit 610 includes a subtraction unit 611, 613, a total voltage control unit 612, an intergroup voltage control unit 614, and an addition unit 615.

The subtraction unit 611 subtracts the total voltage evaluation value Vcgall generated by the voltage evaluation value generation unit 700 from the total voltage command value Vc *. The total voltage command value Vc * is a reference value of the capacitor voltage Vc corresponding to the reference value of the stored energy in the capacitor 32 in each converter cell 7. The total voltage control unit 612 generates the first current command value Izref1 by performing an operation on the deviation of the total voltage evaluation value Vcgall with respect to the total voltage command value Vc * calculated by the subtraction unit 611. The first current command value Izref1 controls the overall level of the capacitor voltage Vc of each converter cell 7 to the total voltage command value Vc *, so that the stored energy in all the converter cells 7 of the power converter 2 is stored. Corresponds to the circulating current value for eliminating the excess or deficiency of.

Similarly, the subtraction unit 613 subtracts the voltage evaluation value Vcgr for each group from the total voltage evaluation value Vcgall. For example, when the basic control unit 502 is the U-phase basic control unit 502, the U-phase voltage evaluation value Vcgu is input to the subtraction unit 613 as the voltage evaluation value Vcgr for each group. The inter-group voltage control unit 614 performs a second calculation on the deviation of the voltage evaluation value Vcgr (U-phase voltage evaluation value Vcgu) for each group with respect to the total voltage evaluation value Vcgall calculated by the subtraction unit 613. Generates the current command value Dev2. The second current command value, Izref2, equalizes the level of the capacitor voltage Vc of the converter cell 7 between the groups (here, between the leg circuits for each phase), and accumulates in the converter cell 7 between the groups. It corresponds to the circulating current value for eliminating the energy imbalance.

For example, the total voltage control unit 612 and the intergroup voltage control unit 614 can be configured as a PI controller that performs proportional calculation and integration calculation on the deviation calculated by the subtraction units 611 and 613, and further differential calculation. It can also be configured as a PID controller that performs the above. Alternatively, the total voltage control unit 612 and the intergroup voltage control unit 614 can be configured by using the configuration of another controller generally used for feedback control.

The addition unit 615 adds the first current command value Izref1 from the total voltage control unit 612 and the second current command value Izref2 from the intergroup voltage control unit 614 to generate a circulating current command value Izref2. ..

The circulation current control unit 605 calculates the circulation control command value Vzp for controlling the circulation current Iz calculated by the circulation current calculation unit 604 to follow the circulation current command value Izref set by the voltage macro control unit 610. The circulating current control unit 605 can also be configured by a controller that executes PI control, PID control, or the like with respect to the deviation of the circulating current Iz with respect to the circulating current command value Izref. That is, the voltage macro control unit 610 using the voltage evaluation value Vcg accumulates in all the converter cells 7 or a plurality of converter cells 7 for each group by forming a minor loop for controlling the circulating current. Suppress excess or deficiency of energy.

In the case of the first embodiment, as will be described later with reference to FIG. 11, the command value changing unit 620 for changing the circulating current command value Izref received from the voltage macro control unit 610 controls the circulating current. A portion 605 is further provided.

The command distribution unit 606 receives an AC control command value Vcp, a circulation control command value Vzp, a DC voltage command value Vdcref, a neutral point voltage Vsn, and an AC voltage Vac. Since the AC side of the power converter 2 is connected to the AC circuit 12 via the transformer 13, the neutral point voltage Vsn can be obtained from the voltage of the DC power supply of the DC circuit 14. The DC voltage command value Vdcref may be given by DC output control or may be a constant value.

The command distribution unit 606 calculates the voltage shared by the upper arm and the lower arm, respectively, based on these inputs. The command distribution unit 606 determines the arm voltage command value krefp of the upper arm and the arm voltage command value krefn of the lower arm by subtracting the voltage drop due to the inductance component in the upper arm or the lower arm from the calculated voltage, respectively. To do.

The determined upper arm arm voltage command value krefp and the lower arm arm voltage command value krefn cause the AC current Iac to follow the AC current command value Iacref, the circulating current Iz to follow the circulating current command value Izref, and direct current. This is an output voltage command that causes the voltage Vdc to follow the DC voltage command value Vdcref and feed-forward controls the AC voltage Vac. In this way, the circulation control command value Vzp for making the circulation current Iz follow the circulation current command value Izref is reflected in the arm voltage command values krefp and krefn. That is, the circulation current command value Izref or the circulation control command value Vzp calculated by the voltage macro control unit 610 is a “control value” that is commonly set for Ncell converter cells 7 included in the same arm. Corresponds to one embodiment.

The basic control unit 502 outputs the arm current Iarmp of the upper arm, the arm current Iarmn of the lower arm, the arm voltage command value krefp of the upper arm, and the arm voltage command value krefn of the lower arm.

FIG. 6 is a block diagram illustrating a configuration example of the arm control unit 503.
With reference to FIG. 6, the arm control unit 503 includes Ncell individual cell control units 202.

The individual cell control unit 202 individually controls the corresponding converter cell 7. The individual cell control unit 202 receives the arm voltage command value kref, the arm current Iarm, and the capacitor voltage command value Vcell * from the basic control unit 502. In the present disclosure, the capacitor voltage command value Vcell * is referred to as an individual voltage command value Vcell * or simply a voltage command value Vcell *.

The individual cell control unit 202 generates the gate signal ga of the corresponding converter cell 7 and outputs it to the corresponding converter cell 7. The gate signal ga is a signal for controlling the on / off of the switching elements 31p and 31n in the converter cell 7 of FIG. 2A (n = 2). When the converter cell 7 has the full bridge configuration shown in FIG. 2B, the gate signals of the switching elements 31p1, 31n1, 31p2, 31n2 are generated (n = 4). On the other hand, the detection value (capacitor voltage Vc) from the voltage detector 33 of each converter cell 7 is sent to the voltage evaluation value generation unit 700 shown in FIG.

FIG. 7 is a block diagram showing a configuration example of the individual cell control unit 202 shown in FIG.
With reference to FIG. 7, the individual cell control unit 202 includes a carrier generator 203, an individual voltage control unit 205, an adder 206, and a gate signal generation unit 207.

The carrier generator 203 generates a carrier signal CS having a predetermined frequency (that is, a carrier frequency) used in phase shift PWM (Pulse Width Modulation) control. The phase shift PWM control shifts the timing of the PWM signals output to each of a plurality of (Ncell) converter cells 7 constituting the same arm (upper arm 5 or lower arm 6). ..

It is known that this reduces the harmonic components included in the combined voltage of the output voltage of each converter cell 7. For example, the carrier generator 203 generates a carrier signal CS that is out of phase with each other among the Ncell converter cells 7 based on the common reference phase θi received from the arm control unit 503.

The individual voltage control unit 205 receives a voltage command value Vcell *, a capacitor voltage Vc of the corresponding converter cell 7, and an arm current of the arm to which the corresponding converter cell 7 belongs. The voltage command value Vcell * can be set to a value (fixed value) common to the voltage command value Vc * of the total voltage control unit 612 of FIG. Alternatively, in order to equalize the capacitor voltage Vc in the same arm, the voltage command value Vcell * may be set to the average value of the capacitor voltages of Ncell converter cells 7 included in the same arm.

The individual voltage control unit 205 calculates the deviation of the capacitor voltage Vc with respect to the voltage command value Vcell * to calculate the control output dkref for individual voltage control. The individual voltage control unit 205 can also be configured by a controller that executes PI control, PID control, or the like. Further, by multiplying the calculated value by the controller by "+1" or "-1" according to the polarity of the arm current Iarm, the capacitor 32 is charged and discharged in the direction of eliminating the deviation. The control output dkref is calculated. Alternatively, the control output dkref for charging / discharging the capacitor 32 in the direction of eliminating the deviation may be calculated by multiplying the calculated value by the controller by the arm current Iarm.

The adder 206 outputs the cell voltage command value krefc by adding the arm voltage command value kref from the basic control unit 502 and the control output dkref of the individual voltage control unit 205.

The gate signal generation unit 207 generates a gate signal ga by PWM-modulating the cell voltage command value krefc by the carrier signal CS from the carrier generator 203.

FIG. 8 is a block diagram showing a detailed configuration example of the individual voltage control unit. With reference to FIG. 8, the individual voltage control unit 205 includes a subtractor 210, a PI controller 211, and a multiplier 213.

The subtractor 210 calculates the deviation of the capacitor voltage Vc with respect to the voltage command value Vcell *. The PI controller 211 performs proportional calculation and integration calculation on the deviation calculated by the subtractor 210. In addition, instead of the PI controller 211, a PID controller that further performs a differential operation may be used, or a feedback controller having another configuration may be used.

The multiplier 213 generates the control output dkref of the individual voltage control unit 205 by multiplying the calculation result of the PI controller 211 by the arm current Iarm. The multiplier 213 may multiply the calculation result of the PI controller 211 by the code "+1" or "-1" according to the polarity of the arm current Iarm instead of the arm current Iarm.

FIG. 9 is a conceptual waveform diagram for explaining PWM modulation control by the gate signal generation unit shown in FIG. 7. The signal waveform shown in FIG. 9 is exaggerated for the sake of explanation, and does not show the actual signal waveform as it is.

With reference to FIG. 9, the cell voltage command value krefc is voltage-compared with the carrier signal CS, which is typically composed of a triangular wave. When the voltage of the cell voltage command value krefc is higher than the voltage of the carrier signal CS, the PWM modulation signal Spwm is set to a high level (H level). On the contrary, when the voltage of the carrier signal CS is higher than the voltage of the cell voltage command value krefc, the PWM modulation signal Spwm is set to the low level (L level).

For example, in the H level period of the PWM modulation signal Spwm, in the converter cell 7 of FIG. 2A, the gate signal ga (n = 2) so as to turn on the switching element 31p while turning off the switching element 31n. Will be generated. On the contrary, in the L level period of the PWM modulation signal Spwm, the gate signal ga (n = 2) is generated so as to turn on the switching element 31n while turning off the switching element 31p.

The switching elements 31p and 31n of the converter cell 7 are on / off controlled by being transmitted as the gate signal ga to the gate driver (not shown) of the switching elements 31p and 31n of the converter cell 7.

The cell voltage command value krefc corresponds to the sinusoidal voltage modified by the control output dkref. Therefore, in the control device 3, the modulation rate command value in PWM modulation is calculated by a known method from the amplitude (or effective value) of the sine wave voltage (arm voltage command value kref) and the amplitude of the carrier signal CS. It is possible.

As described above, in the power converter according to the present embodiment, the capacitor voltage Vc of the converter cell 7 is individually controlled for each converter cell 7 (individual voltage control unit 205) and the entire power converter 2. Alternatively, it is understood that the control is performed in multiple layers with a macro control (voltage macro control unit 610) for controlling the stored energy in a plurality of converter cells 7 in the same group (each phase leg circuit or arm). To.

(Cause of capacitor voltage variation in individual control)
The voltage macro control unit 610 of FIG. 5 causes excess or deficiency of stored energy in all converter cells 7 of the power converter 2 and imbalance of stored energy between groups (between each phase leg circuit or between arms). Even if the above is corrected, the individual control in the individual cell control unit 202 may not function sufficiently and the individual capacitor voltage Vc may vary. As a result, the capacitor voltage Vc of any of the converter cells 7 may be over-rise or over-lower to the level of overvoltage protection or undervoltage protection, and the operation of the MMC may be stopped.

One of the causes of the variation of the individual capacitor voltage Vc as described above is that the arm current Iarm is extremely small. For example, the arm current Iarm becomes small when the AC power input or output between the AC circuit 12 and the power conversion device 1 is small. As the arm current Iarm becomes smaller, the current flowing through each converter cell 7 becomes smaller, so that the current that charges the power storage element 32 or is discharged from the power storage element 32 also becomes smaller. As a result, individual control becomes difficult to work, and individual capacitor voltages Vc vary. If the variation of the individual capacitor voltage Vc is left unattended, the variation may further increase.

In the power conversion device 1 of the first embodiment, when the individual capacitor voltage Vc varies widely, the circulating current is increased while being controlled by the AC current control unit 603 (that is, the absolute value of the circulating current command value is increased). ) To control the power converter 2. As a result, the effective value of the current flowing through each converter cell 7 can be increased without affecting the control of the input / output of AC power between the power converter 2 and the AC circuit 12. As a result, the individual control can be easily effective and the variation of the capacitor voltage Vc can be suppressed. Hereinafter, a specific description will be given with reference to FIGS. 10 to 12.

(Configuration and operation of circulating current changer)
FIG. 10 is a block diagram showing a configuration example of the circulating current changing unit 810. The circulating current changing unit 810 is provided in the control device 3. The circulating current changing unit 810 outputs a changing command of the circulating current command value Izref to the circulating current control unit 605.

As shown in FIG. 10, the circulating current changing unit 810 includes a maximum / minimum generating unit 811 that receives the capacitor voltage Vc detected by the voltage detector 33 in each converter cell 7, and a command value changing command unit 812. .. The maximum / minimum generation unit 811 obtains the maximum value Vcmax and the minimum value Vcmin of the capacitor voltage Vc of all the converter cells 7. When the difference between the maximum value Vcmax and the minimum value Vcmin is larger than the threshold value, the command value change command unit 812 issues a command value change command unit 620 provided in the circulation current control unit 605 to change the circulation current command value Isref. Output.

FIG. 11 is a block diagram showing a configuration example of the circulating current control unit including the function of changing the circulating current command value. With reference to FIG. 11, the circulating current control unit 605 includes a command value changing unit 620, a subtractor 621, and a PI controller 622. The circulating current control unit 605 of FIG. 11 is different from the circulating current control unit 605 of FIG. 5 in that the command value changing unit 620 is further included.

When the command value changing unit 620 receives a command for changing the circulating current command value Isref from the command value changing command unit 812 of the circulating current changing unit 810, for example, the circulating current command value Isref input from the voltage macro control unit 610. The change amount ΔIz is added to, and the addition result is output to the subtractor 621 as the final circulating current command value Izref *. On the other hand, when the command value change unit 620 has not received the change command of the circulating current command value Izref from the command value change command unit 812, the command value changing unit 620 outputs the input circulating current command value Izref as Izref * without changing it as it is. To do.

The subtractor 621 calculates the deviation between the circulating current command value Izref * output from the command value changing unit 620 and the circulating current Iz calculated by the circulating current calculation unit 604. The PI controller 622 performs proportional calculation and integration calculation on the deviation calculated by the subtractor 621. In addition, instead of the PI controller 622, a PID controller that further performs a differential calculation may be used, or a feedback calculator having another configuration may be used. The circulation current control unit 605 outputs the calculation result of the PI controller 622 as the circulation control command value Vzp.

FIG. 12 is a flowchart showing the operation of the command value change command unit of FIG. With reference to FIG. 12, the command value change command unit 812 operates when the difference between the maximum value Vcmax and the minimum value Vcmin of the capacitor voltage Vc of all the converter cells 7 is larger than the threshold value Vth1 (in step S600). YES). The command value change command unit 812 stores the circulating current command value Izref received from the voltage macro control unit 610 at the time when step S600 becomes YES as Izref 0 in the memory (step S605). In this case, the command value change command unit 812 changes the command value so as to change the circulating current command value Izref received from the voltage macro control unit 610 to Izref 0 + ΔIz, that is, to increase the absolute value of the circulating current command value Izref. Command unit 620 (step S610).

The circulation current control unit 605 generates a circulation control command value Vzp based on the changed circulation current command value Izref0 + ΔIz (= Izref *) and the circulation current Iz calculated from the arm current Iarm. Since the arm voltage command value kref is generated based on the calculated circulation control command value Vzp, as a result, the circulating current of each phase of the power converter 2 increases. Then, the arm current Iarm can be increased by the increase in the circulating current.

After that, when the difference between the maximum value Vcmax and the minimum value Vcmin of the capacitor voltage Vc of all the converter cells 7 becomes smaller than the threshold value Vth2 (however, Vth2 <Vth1), the command value change command unit 812 (step). YES in S620), instructing the command value changing unit 620 of the circulating current control unit 605 to return the circulating current command value changed in step S610 (step S630). If NO in step S620, step S610 is repeated.

(Modification example)
When the circulating current is increased, the difference in the capacitor voltage Vc between the arms may become too large. Therefore, in order to eliminate the difference in the capacitor voltage Vc between the arms, the above-mentioned circulation current command value Izref may be changed intermittently. For example, the command value change command unit 812 commands the command value change unit 620 to alternately repeat the case where the circulating current command value Izref is changed to Izref0 + ΔIz and the case where the original circulating current command value Izref0 is not changed. ..

Alternatively, the circulating current command value Izref may be set so as to alternately change the direction in which the arm current Iarm flows. For example, the command value change command unit 812 alternately repeats the case of adding the change amount ΔIz to the original circulating current command value Izref0 and the case of subtracting the change amount ΔIz from the original circulating current command value Izref0. Command the change unit 620.

The maximum / minimum generation unit 811 may obtain the maximum value and the minimum value after applying a high frequency removal filter to the time series data of the capacitor voltage Vc of each input converter cell 7.

Further, instead of the difference between the maximum value Vcmax and the minimum value Vcmin of the capacitor voltage Vc, the dispersion or standard deviation of the capacitor voltage Vc of all the converter cells 7 may be used, and is an evaluation value indicating the degree of variation. If there is, there is no particular limitation. Therefore, the command value change command unit 812 changes the command value to change the circulating current command value Izref input from the voltage macro control unit 610 to Izref0 + ΔIz when the evaluation value indicating the degree of variation is larger than the threshold value. Output to unit 620.

(Effect of Embodiment 1)
As described above, according to the power converter 1 of the first embodiment, when the variation of the capacitor voltage Vc of each converter cell 7 is large, the circulating current command value Isref is set to a larger value. As a result, the effective value of the arm current Iarm increases as the circulating current increases, so that the individual control functions more effectively. As a result, variations in individual capacitor voltages Vc can be suppressed.

Embodiment 2.
In the power converter 1 of the second embodiment, the phase adjusting device 801 is connected between the AC circuit 12 and the power converter 2. When the variation of the individual capacitor voltage Vc is large, the effective value of the arm current Iarm is increased by passing a reactive current from the power converter 2 to the phase adjusting device 801. As a result, individual control becomes effective, and variations in the capacitor voltage Vc can be suppressed. Hereinafter, a specific description will be given with reference to FIGS. 13 to 15.

FIG. 13 is a schematic configuration diagram of the power conversion device of the second embodiment. With reference to FIG. 13, in the power converter 1B of the second embodiment, the phase adjusting device 801 is connected to the AC line between the power converter 2 and the AC circuit 12 via the switch 802. , Different from the power converter 1 of FIG.

Here, the connection position of the switch 802 is between the alternating current detector 16 and the transformer 13. Therefore, the phase adjusting device 801 causes the power converter 2 to output a reactive current, but does not affect the current control and the voltage control of the AC circuit 12.

The phase adjusting device 801 may be connected to the AC line by a Y connection or may be connected by a Δ connection. Further, although FIG. 13 shows an example of the capacitance of the phase adjustment device 801 composed of a capacitor, a filter, or the like, it may be an inductive phase adjustment device such as a reactor. Since the other points of FIG. 13 are the same as those of FIG. 1, the same or corresponding parts are designated by the same reference numerals and the description is not repeated.

FIG. 14 is a block diagram showing a configuration example of a phase adjustment device control unit that controls the operation of the phase adjustment device of FIG. 13. The phase adjusting device control unit 820 is provided in the control device 3. The phase adjustment device control unit 820 operates the phase adjustment device 801 by turning on the switch 802 of FIG. 13 when the variation of the individual capacitor voltage Vc is large. As shown in FIG. 14, the phase adjustment device control unit 820 includes a maximum / minimum generation unit 821 and a switch control unit 822.

The maximum / minimum generation unit 821 receives the capacitor voltage Vc detected by the voltage detector 33 in each converter cell 7. The maximum / minimum generation unit 821 obtains the maximum value Vcmax and the minimum value Vcmin of the capacitor voltage Vc of all the converter cells 7. The maximum / minimum generation unit 821 outputs the obtained information on the maximum value Vcmax and the minimum value Vcmin to the switch control unit 822.

FIG. 15 is a flowchart showing an operation example of the switch control unit of FIG. With reference to FIG. 15, the switch control unit 822 operates when the difference between the maximum value Vcmax and the minimum value Vcmin of the capacitor voltage Vc of all the converter cells 7 is larger than the threshold value Vth1 (YES in step S700). To do. In this case, the switch control unit 822 connects the phase adjustment device 801 to the power converter 2 by turning on the switch 802 (step S710). As a result, the reactive current flows from the power converter 2 to the phase adjusting device 801, so that the arm current Iarm can be increased. As a result, the individual control functions effectively, so that the variation of the individual capacitor voltage Vc can be suppressed.

After that, when the difference between the maximum value Vcmax and the minimum value Vcmin of the capacitor voltage Vc of all the converter cells 7 becomes smaller than the threshold value Vth2 (however, Vth2 <Vth1) (YES in step S720), the switch control unit 822 , The phase adjustment device 801 is separated from the power converter 2 by opening the switch 802 that was turned on in step S710 (step S730).

As described above, according to the power converter 1B of the second embodiment, when the capacitor voltage Vc of each converter cell 7 varies widely, the phase adjusting device 801 is electrically connected to the power converter 2. This causes the ineffective current to flow through the power converter 2. As a result, the effective value of the arm current Iarm becomes large, so that individual control becomes effective. As a result, variations in individual capacitor voltages Vc can be suppressed.

In step S700 of FIG. 15, instead of the difference between the maximum value Vcmax and the minimum value Vcmin of the capacitor voltage Vc, the dispersion or standard deviation of the capacitor voltage Vc of all the converter cells 7 and the like are used for each capacitor voltage Vc. An evaluation value indicating the degree of variation may be used.

Embodiment 3.
In the power conversion device of the third embodiment, the transformer 13 connected between the AC circuit 12 and the power converter 2 of FIG. 1 has a function of switching taps by an external command. When the variation of the individual capacitor voltage Vc is large, the transformation ratio of the transformer 13 is changed by switching the taps of the transformer 13. Hereinafter, a specific description will be given with reference to the drawings. The other hardware configuration of the power conversion device 1 of FIG. 1 is also applied to the case of the third embodiment.

FIG. 16 is a block diagram showing a configuration example of a transformer control unit for controlling switching of taps of the transformer of FIG. 1. The transformer control unit 830 is provided in the control device 3. As shown in FIG. 16, the transformer control unit 830 includes a maximum / minimum generation unit 831 and a tap changer command unit 832.

The maximum / minimum generation unit 831 receives the capacitor voltage Vc detected by the voltage detector 33 in each converter cell 7. The maximum / minimum generation unit 831 obtains the maximum value Vcmax and the minimum value Vcmin of the capacitor voltage Vc of all the converter cells 7. The maximum / minimum generation unit 831 outputs the obtained information on the maximum value Vcmax and the minimum value Vcmin to the tap switching command unit 832.

FIG. 17 is a flowchart showing an operation example of the tap changer command unit of FIG. With reference to FIG. 17, the tap changer command unit 832 operates when the difference between the maximum value Vcmax and the minimum value Vcmin of the capacitor voltage Vc of all the converter cells 7 is larger than the threshold value Vth1 (YES in step S800). To do. In this case, the tap changer command unit 832 outputs the tap changer command to the transformer 13 (step S810). As a result, the transformation ratio of the transformer 13 is changed, and the effective value of the alternating current on the power converter 2 side increases. As the effective value of the AC current Iac increases, the effective value of the arm current Iarm of the power converter 2 also increases, so that individual control becomes more effective. As a result, variations in individual capacitor voltages Vc can be suppressed.

The AC current control unit 603 of the power conversion device 1 controls the AC current Iac on the AC circuit 12 side so as to be equal to the AC current command value Iacref. Therefore, changing the transformer ratio of the transformer 13 does not affect the voltage control and the current control on the AC circuit 12 side.

After that, when the difference between the maximum value Vcmax and the minimum value Vcmin of the capacitor voltage Vc of all the converter cells 7 becomes smaller than the threshold value Vth2 (however, Vth2 <Vth1) (YES in step S820), the tap switching command unit 832 , Instruct the transformer 13 to return the tap of the transformer 13 changed in step S810 (step S830).

As described above, according to the power converter of the third embodiment, when the variation of the capacitor voltage Vc of each converter cell 7 is large, the transformer provided between the power converter 2 and the AC circuit 12 is provided. The transformation ratio of the transformer 13 is changed by switching the taps of the capacitor 13. As a result, the AC current on the power converter 2 side can be increased without affecting the AC circuit 12 side. As a result, the arm current Iarm becomes large and the individual control becomes effective, so that the variation of the individual capacitor voltage Vc can be suppressed.

In step S800 of FIG. 17, instead of the difference between the maximum value Vcmax and the minimum value Vcmin of the capacitor voltage Vc, the dispersion or standard deviation of the capacitor voltage Vc of all the converter cells 7 and the like are used for each capacitor voltage Vc. An evaluation value indicating the degree of variation may be used.

Embodiment 4.
In the power conversion device of the fourth embodiment, when the variation of the individual capacitor voltage Vc is large, the alternating current supplied from the power converter 2 to the alternating current circuit 12 includes a negative phase current component. As a result, the effective value of the alternating current increases by the amount of the reverse phase current, and the effective value of the arm current also increases, so that the individual control of the capacitor voltage Vc functions effectively. Hereinafter, a specific description will be given with reference to the drawings. The configuration of the power conversion device 1 of the first embodiment is basically applied to the case of the fourth embodiment except for the alternating current control unit 603.

FIG. 18 is a block diagram showing a configuration example of a reverse phase current control unit for controlling a negative phase current supplied from the power converter to the DC circuit. The reverse phase current control unit 840 is provided in the control device 3. As shown in FIG. 18, the reverse phase current control unit 840 includes a maximum / minimum generation unit 841 and a command value change command unit 842.

The maximum / minimum generation unit 841 receives the capacitor voltage Vc detected by the voltage detector 33 in each converter cell 7. The maximum / minimum generation unit 841 obtains the maximum value Vcmax and the minimum value Vcmin of the capacitor voltage Vc of all the converter cells 7. When the difference between the maximum value Vcmax and the minimum value Vcmin is larger than the threshold value, the command value change command unit 842 sets the reverse phase current amount within the specified range in the command value change unit 630 provided in the AC current control unit 603. Is instructed to be included in the AC current command value Iacref.

FIG. 19 is a block diagram showing a configuration example of an AC current control unit in the power conversion device of the fourth embodiment. With reference to FIG. 19, the AC current control unit 603 includes a command value changing unit 630, a subtractor 631, and a PI controller 632. The AC current control unit 603 of FIG. 19 is different from the AC current control unit 603 of FIG. 5 in that the command value changing unit 630 is further included.

When the command value change unit 630 receives a change command of the AC current command value Iacref from the command value change command unit 842 of the reverse phase current control unit 840, the reverse phase current component is within the specified range in the AC current command value Iacref. Include in. Then, the command value changing unit 630 outputs the changed AC current command value Iacref * to the subtractor 631. On the other hand, when the command value change unit 630 does not receive the change command of the AC current command value Iacref from the command value change command unit 842, the command value change unit 630 outputs the input AC current command value Iacref as Iacref * without changing it as it is. To do.

The subtractor 631 calculates the deviation between the AC current command value Iacref * output from the command value changing unit 630 and the detected AC current Iac. The PI controller 632 performs proportional calculation and integration calculation on the deviation calculated by the subtractor 631. In addition, instead of the PI controller 632, a PID controller that further performs a differential calculation may be used, or a feedback calculator having another configuration may be used. The AC current control unit 603 outputs the calculation result of the PI controller 632 as an AC control command value Vcp.

FIG. 20 is a flowchart showing an operation example of the command value change command unit of FIG. With reference to FIG. 20, when the difference between the maximum value Vcmax and the minimum value Vcmin of the capacitor voltage Vc of all the converter cells 7 is larger than the threshold value Vth1 (YES in step S900), the command value change command unit 842 Operate. In this case, the command value change command unit 842 commands the command value change unit 630 of the AC current control unit 603 to include the reverse phase current in the AC current command value Iacref (step S910).

The AC current control unit 603 calculates the deviation between the AC current command value Iacref * after being changed by the command value changing unit 630 and the detected AC current Iac by a feedback calculator such as a PI calculator. By applying, the AC control command value Vcp is calculated. Since the arm voltage command value kref is generated based on the calculated AC control command value Vcp, the power converter 2 outputs the AC current Iac including the reverse phase current to the AC circuit 12. As a result, the effective value of the arm current Iarm is increased by the increased reverse phase current, so that the individual control functions more effectively and the variation of the individual capacitor voltage Vc can be suppressed.

After that, when the difference between the maximum value Vcmax and the minimum value Vcmin of the capacitor voltage Vc of all the converter cells 7 becomes smaller than the threshold value Vth2 (however, Vth2 <Vth1) (YES in step S920), the command value change command unit 842 Command the command value changing unit 630 of the AC current control unit 603 to restore the AC current command value Iacref changed in step S910 (step S930).

As described above, according to the power converter of the fourth embodiment, when the variation of the capacitor voltage Vc of each converter cell 7 is large, the AC current Iac supplied from the power converter 2 to the AC circuit 12 is applied. The reverse phase current is included. As a result, the effective value of the alternating current Iac increases by the amount of the reverse phase current, so that the effective value of the arm current Iarm also increases. As a result, the individual control of the capacitor voltage Vc becomes effective, so that the variation of the individual capacitor voltage Vc can be suppressed.

In step S900 of FIG. 20, instead of the difference between the maximum value Vcmax and the minimum value Vcmin of the capacitor voltage Vc, the dispersion or standard deviation of the capacitor voltage Vc of all the converter cells 7 and the like are used for each capacitor voltage Vc. An evaluation value indicating the degree of variation may be used.

Embodiment 5.
In the fifth embodiment, a case where the above-described embodiments 1 to 4 are more generalized will be described. In addition, Embodiments 1 to 4 can be combined appropriately.

21 shows a configuration example of a generalized control changing unit of the circulating current changing unit of FIG. 10, the phase adjusting device control unit of FIG. 13, the transformer control unit 830 of FIG. 15, and the reverse phase current control unit of FIG. It is a block diagram which shows. The control change unit 850 is provided in the control device 3 and suppresses variations in individual capacitor voltages. As shown in FIG. 21, the control change unit 850 includes a variation evaluation value generation unit 851 and a change command unit 852.

The variation evaluation value generation unit 851 corresponds to the maximum / minimum generation units 811, 821, 831, 841 of FIGS. 10, 14, 16, and 18. The variation evaluation value generation unit 851 receives the capacitor voltage Vc detected by the voltage detector 33 in each converter cell 7 and generates an evaluation value indicating the degree of variation of each capacitor voltage Vc. The evaluation value is, for example, the difference, variance, or standard deviation between the maximum value Vcmax and the minimum value Vcmin.

The change command unit 852 corresponds to the command value change command unit 812 of FIG. 10, the switch control unit 822 of FIG. 14, the tap change command unit 832 of FIG. 16, and the command value change command unit 842 of FIG. When the above evaluation value exceeds the threshold value Vth1, the change command unit 852 executes AC control by the AC current control unit 603 of FIG. 5 and individual control of the capacitor voltage Vc by the individual voltage control unit 205 of FIG. However, the control of the power converter 2 is changed so as to increase the effective value of the arm current Iarm. As a result, the individual control of the capacitor voltage Vc becomes effective without affecting the current control and the voltage control of the AC circuit 12, so that the variation of the individual capacitor voltage Vc can be suppressed.

FIG. 22 is a flowchart showing an operation example of the change command unit of FIG. 21. With reference to FIG. 22, the change command unit 852 operates when the variation evaluation value of the capacitor voltage Vc of all the converter cells 7 is larger than the threshold value Vth1 (YES in step S1000). In this case, the change command unit 852 increases the effective value of the arm current Iarm while executing the AC control by the AC current control unit 603 of FIG. 5 and the individual control of the capacitor voltage Vc by the individual voltage control unit 205 of FIG. 7. The control of the power converter 2 is changed so as to (step S1010).

After that, when the variation evaluation value of the capacitor voltage Vc of all the converter cells 7 becomes smaller than the threshold value Vth2 (however, Vth2 <Vth1) (YES in step S1020), the change command unit 852 controls the power converter 2. Undo (step S1020).

The embodiments disclosed this time should be considered as exemplary in all respects and not restrictive. The scope of this application is indicated by the scope of claims rather than the above description, and is intended to include all modifications within the meaning and scope of the claims.

1,1B power converter, 2 power converter, 3 controller, 4 leg circuit, 5 upper arm, 6 lower arm, 7 converter cell, 9A, 9B arm current detector, 10 AC voltage detector, 11A, 11B DC voltage detector, 12 AC circuit, 13 transformer, 14 DC circuit, 16 AC current detector, 17 DC current detector, 31 switching element, 32 power storage element (capacitor), 33 voltage detector, 74 CPU, 202 individual Cell control unit, 203 carrier generator, 205 individual voltage control unit, 207 gate signal generation unit, 211, 622,632 PI controller, 501 switching control unit, 502 basic control unit, 503 arm control unit, 601 arm voltage command generation Unit, 603 AC current control unit, 604 AC current calculation unit, 605 Circulation current control unit, 606 Command distribution unit, 610 Voltage macro control unit, 612 Total voltage control unit, 614 Intergroup voltage control unit, 620, 630 Command value change Unit, 700 Voltage evaluation value generator, 801 phase adjustment device, 802 switch, 810 circulating current change section, 811,821,831,841 maximum / minimum generator, 812,842 command value change command section, 820 phase adjustment device Control unit, 822 switch control unit, 830 transformer control unit, 832 tap switching command unit, 840 reverse phase current control unit, 850 control change unit, 851 variation evaluation value generation unit, 852 change command unit, Iacref AC current command value , Iac AC current, Iarm arm current, Iz circulating current, Izref circulating current command value, P1, P2 input / output terminals, Vac AC voltage, Vc * total voltage command value, Vc capacitor voltage, Vcell * individual voltage command value, Vcgal all Voltage evaluation value, voltage evaluation value for each Vcgr group, Vcp AC control command value, Vth1, Vth2 threshold, Vzp circulation control command value.

Claims (8)

It ’s a power converter,
A power converter including a plurality of arms having a plurality of converter cells cascaded to each other.
Each of the plurality of arms is electrically connected to the corresponding phase of the AC circuit.
Each of the plurality of converter cells
A pair of input / output terminals and
With multiple switching elements
A power storage element that is electrically connected to the input / output terminal via the plurality of switching elements.
It has a voltage detector that detects the voltage of the power storage element.
The power converter further
An AC current detector that detects an AC current flowing through an AC line connecting the AC circuit and the power converter, and
A control device for controlling the power converter is provided.
The control device is
An AC current control unit that controls AC current according to the deviation between the detected AC current and the AC current command value, and
An individual voltage control unit that performs individual voltage control according to the deviation between the voltage of each storage element and the individual voltage command value, and
An evaluation value indicating the degree of voltage variation of the power storage element in the entire power converter is calculated, and when the evaluation value is larger than the threshold value, the AC current control and the individual voltage control are executed. A power conversion device including a control change unit that changes the control of the power converter so that the effective value of the arm current flowing through the plurality of arms is increased. The power conversion device further includes a plurality of arm current detectors that detect arm currents flowing through the plurality of arms.
The control device is
Circulating current control according to the deviation between the circulating current calculated based on the detected arm current and the circulating current command value calculated based on the average value of the voltages of the power storage elements in the plurality of converter cells. Including a circulating current control unit that performs
The control changing unit according to claim 1, wherein when the evaluation value is larger than the threshold value, the control changing unit outputs a command to change the absolute value of the circulating current command value to a larger value to the circulating current control unit. Power converter. 2. The control changing unit outputs a command to intermittently change the absolute value of the circulating current command value to a larger value when the evaluation value is larger than the threshold value. The power converter described. When the evaluation value is larger than the threshold value, the control change unit alternates between adding the change amount to the original circulating current command value and subtracting the change amount from the original circulating current command value. The power conversion device according to claim 2, wherein a command to be repeated is output to the circulating current control unit. Further, a phase adjusting device connected to the AC line via a switch between the AC current detector and the power converter is provided.
The power conversion device according to any one of claims 1 to 4, wherein the control changing unit outputs a command to turn on the switch when the evaluation value is larger than the threshold value. Further equipped with a transformer with a tap switching function connected between the alternating current detector and the power converter.
Any of claims 1 to 5, wherein the control change unit increases the alternating current on the power converter side by outputting a switching command for the tap of the transformer when the evaluation value is larger than the threshold value. The power converter according to item 1. When the evaluation value is larger than the threshold value, the control change unit outputs a command for changing the AC current command value to include the reverse phase current to the AC current control unit.
The power conversion device according to any one of claims 1 to 6, wherein the AC current control unit controls an AC current according to a deviation between the detected AC current and the changed AC current command value. .. It ’s a power converter,
A power converter including a plurality of arms having a plurality of converter cells cascaded to each other.
Each of the plurality of arms is electrically connected to the corresponding phase of the AC circuit.
Each of the plurality of converter cells
A pair of input / output terminals and
With multiple switching elements
A power storage element that is electrically connected to the input / output terminal via the plurality of switching elements.
It has a voltage detector that detects the voltage of the power storage element.
The power converter further
An AC current detector that detects an AC current flowing through an AC line connecting the AC circuit and the power converter, and
A control device for controlling the power converter is provided.
The control device is
An AC current control unit that controls AC current according to the deviation between the detected AC current and the AC current command value, and
An individual voltage control unit that performs individual voltage control according to the deviation between the voltage of each storage element and the individual voltage command value, and
An evaluation value indicating the degree of voltage variation among the individual power storage elements is calculated, and when the evaluation value is larger than the threshold value, the plurality of arms are executed while performing the AC current control and the individual voltage control. A power conversion device including a control change unit that changes the control of the power converter so that the effective value of the arm current flowing through the power converter is increased.

Images